In a long-term evolution LTE (4G network) system, an evolved universal terrestrial radio access network (E-UTRAN) is composed of a plurality of base stations eNodeb, an eNodeB and an Evolved Packet Core (EPC, 4G core network) are connected through an S1 (between the base station and the packet core network EPC) interface, and the eNodeBs are connected through an X2 (inter-base station) interface. In a 5G system, upon consideration of introducing a central unit for centralized control and scheduling, a function of radio resource control (RRC) and a function of part of layers, i.e., layer 2 (data link layer) or/and layer 1 (physical layer), are deployed at the central node, and other functions of the base station are deployed at distribute units. The interface (NG) of the base station and the core network in the 5G network is terminated in the central unit (CU), and the interface (Xn) between the base stations is also terminated in the CU.
Possible ways of separating the central unit (CU)/distributed unit (DU) on the radio access network (RAN) side and the transport layer protocol of the current wired interface will be briefly described below.
1) RAN Side Architecture
Two possible 5G network deployment structures are provided below.
Deployment structure 1: base station+user equipment
Shown in FIG. 1 is a typical LTE architecture. There are multiple cells under an eNB. In a connected state, user equipment (UE) and the cell perform radio data transmission and reception.
Deployment structure 2: As shown in FIG. 2, the network side node is divided into a central unit (CU) and a distributed unit (DU), the user side node is a user equipment (UE), and information interaction is performed between the UE and the DU through transmission points TRP.
2) 5G Transport Layer Protocol of Wired Interface (NG, Xn)
Considering that an interface control signaling requires high reliability, the control plane adopts a Stream Control Transmission Protocol (SCTP), as shown in FIG. 3.
As shown in FIG. 4, the user plane mainly adopts a GTP-U protocol (point-to-point tunneling protocol), which, mainly considering the protocol specifications defined internally in 3GPP, is advantageous for compatibility with the original system. However, GTP-U does not guarantee reliable transmission.
3) Separation Between CU and DU on the RAN Side:
In the deployment architecture 2, the way of separating the CU from the DU on the RAN side needs to be taken into consideration. Currently, there are 8 possible options, as shown in FIG. 5:
Option 1: RRC in the CU; packet data convergence protocol PDCP, radio link control protocol RLC, medium access control protocol MAC, physical layer, and radio frequency RF in the DU;
Option 2: RRC, and PDCP in the CU; RLC, MAC, physical layer, and RF in the DU;
Option 3: RRC, PDCP, and RLC high layer (High-RLC, RLC-H) in the CU; RLC low layer (Low-RLC, RLC-L), MAC, physical layer, and RF in the DU;
Option 4: RRC, PDCP, and RLC in the CU; MAC, physical layer, and RF in the DU;
Option 5: RRC, PDCP, RLC, and MAC high layer (High-MAC) in the CU; MAC low layer (Low-MAC), physical layer, and RF in the DU;
Option 6: RRC, PDCP, RLC, and MAC in the CU; physical layer and RF in the DU;
Option 7: RRC, PDCP, RLC, MAC, and part of physical layer (high layer of physical layer, High-PHY) in the CU; low layer of physical layer (Low-PHY) and RF in the DU;
Option 8: RRC, PDCP, RLC, MAC and physical layer in the CU; RF in the DU.
However, as for the above solutions for separation of the CU from the DU, the related art does not address how the data stream corresponding to the RRC message is transmitted through the interface between the CU and the DU, so that the data cannot be correctly transmitted.